In the motor industry, there has been a trend to use electronic ignition systems to improve the efficiency and performance of internal combustion engines by producing a spark with desired characteristics to initiate combustion of the air-fuel mixture.
Nevertheless, in the case of capacitative discharge systems, where sufficient spark voltage can build up in a relatively short period, it has been found that the spark produced by the spark voltage is of relatively short duration. Such operation characteristics are even more particularly so in a capacitative discharge ignition system having a low-capacitance high-voltage charge storage means or capacitor.
The high-voltage will cause a high discharging current passing through the primary coil to induce the necessary spark voltage in the secondary coil to produce the spark. However, the low-capacitance limits the duration of that current and thus, the duration of the spark as produced.
It has been realised that the spark duration may sometimes be too brief to properly ignite the air-fuel mixture, particularly for a lean mixture.
A proposal to merely increase the capacitance of the charge storage means or capacitor would not significantly extend the spark duration, but rather would cause a more intense spark. Another proposal to provide a resistor in the primary circuit to reduce the rate of discharge would also reduce the amount of the discharging current and the energy available for the spark.
Further, the use of transistors of the type called silicon controlled rectifiers to initiate the discharge of energy from the charge storage means or capacitor would invariably allow the energy which has been stored in the primary coil during the discharge to dissipate within the primary circuit.